On 2012-05-14, at 07:37, Gerrit Heitsch wrote: >> http://dl.dropbox.com/u/58002657/y_c_amp.png > > He... considering that the original circuit was an image published on the forum64.de website. I just made it into ASCII so it can be easily posted. Your ASCII-art skills are remarkable in this context. I re-captured it in order to prepare for the pcb. Do you happen to have link to the original post on forum64.de? > An important detail... On the 250466 I tried this on, I had thought about using the modulator supply, but there it does not run on +5V but the unregulated +9V. So I grabbed +5V from trace feeding the expansion port. This means it will not really be possible to put it into the modulator housing unless you also add a 78L05 plus support. I know, But +5V is available in multiple places around the mainboard. I shall tap to one of the available points as I believe one wire more over my particular board won't do much harm ;-) >> Now I shall need the actual dimensions of the modulator case (I am out of my place) and I can quickly lay a pcb out of this. One that would go exactly in place of the modulator and connect directly to its solder points. > > I just removed the modulator completly and put a small handwired PCB in its place. I never thought about making a PCB for something as small as this circuit. Even if I like PCBs, for this thing alone I wouldn't probably do either. But I find your idea about removing the modulator very much appealing also for another reason: For some time I want to rebuild the audio part of the machine. Silencing the noise, putting in second SID, amplifier, micro speakers and stereo RCA sockets to the outside. The last being something I am long time reluctant to drill another set of holes in the upper casing for. But this idea of taking away the modulator not only makes ample room available but also gives me ready to use rear panel space on the lower casing! Even with one hole being ready for RCA socket OOB ;-) So the PCB is going to be more complex in the end than those few elements alone would require. >> Tried what works better in such case? Or is it 470 for VIC and 1k for TED? > > So far I have only built one for a C16 and there the 470 Ohm seem to work. Have you noticed tangible improvement in picture quality? > Feel free to check with 1 KOhm, it means TED will have to sink less current. I need it for VIC (C64). But I believe the same applies. Shall check. >>> Do _not_ use metal film resistors, >> >> Why? > > Because they are a metal film with a spiral groove in it. Which is sufficiently close to a coil that it will act as one once the frequency gets high enough (This circuit goes up into the MHz range). The effects are not very big but enough to influence the picture quality. I see, thanks. But this applies not only to metal film. Carbon film, wire, ... , doesn't it? So I guess the safest bet is a carbon comp. or similar. > Well, the 2114 and derivates are old chips that are not made anymore and no one uses in new designs anymore... So you have to look where old chips are sold. > > Like here: > > http://www.ebay.de/itm/290695335618 Thank you Gerrit! I truly appreciate your inputs and willingness to share and help. BTW. I checked again the temperatures of the elements. Next to VRs and VIC, the next biggest "heat offenders" are SID and PLA. I even placed some self adhesive radiators on them some years ago. Especially SID gets really hot. Then the next is CHAROM. Don't know why. BASIC doesn't get so hot. But this makes me think about this +12V you took down to 10.. Since both boiling plates (VIC and SID) use the +12, would lowering it in general allow SID still to work but dissipate less heat? Would it have any adverse effect elsewhere? Shall have to check.. -- SD! Message was sent through the cbm-hackers mailing listReceived on 2012-05-14 11:00:07
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